Cu_1.8S has been considered as a potential thermoelectric (TE) material for its stable electrical and thermal properties, environmental benignity, and low cost. Herein, the TE properties of nanostructured Cu_1.8S_1-xTe_x (0 ≤ x ≤ 0.2) bulks fabricated by a facile process combining mechanical alloying (MA) and room-temperature high-pressure sintering (RT-HPS) technique were optimized via eliminating the volatilization of S element and suppressing grain growth. Experimentally, a single phase of Cu_1.8S was obtained at x = 0, and a second Cu_1.96S phase formed in all Cu_1.8S_1-xTe_x samples when 0.05 ≤ x ≤ 0.125. With further increasing x to 0.15 ≤ x ≤ 0.2, the Cu_2-zTe phase was detected and the samples consisted of Cu_1.8S, Cu_1.96S, and Cu_2-zTe phases. Benefiting from a modified band structure and the coexisted phases of Cu_1.96S and Cu_2-zTe, the power factor is enhanced in all Cu_1.8S_1-xTe_x (0.05 ≤ x ≤ 0.2) alloys. Combining with a drastic decrease in the thermal conductivity due to the strengthened phonon scatterings from multiscale defects introduced by Te doping and nano-grain boundaries, a maximum figure of merit (ZT) of 0.352 is reached at 623 K for Cu_1.8S_0.875Te_0.125, which is 171% higher than that of Cu_1.8S (0.130). The study demonstrates that doping Te is an effective strategy to improve the TE performance of Cu_1.8S based materials and the proposed facile method combing MA and RT-HPS is a potential way to fabricate nanostructured bulks.